1. Field of the Invention
The present invention relates to distortion-compensated amplifying circuits. More specifically, the present invention relates to a distortion-compensated amplifying circuit that is used typically in a mobile communications base station for cellular phones and is capable of amplifying a signal and compensating for distortion that occurs at the time of amplification.
2. Description of the Background Art
In recent years, a transmission apparatus at a base station for mobile communications devices collectively amplifies a large number of signal channels, requiring a highly-efficient, more linear power amplifier. To increase the linearity of such a power amplifier, an amplifying circuit capable of compensating for distortion has to be adopted.
FIG. 17 shows one exemplary configuration of a conventional distortion-compensated amplifying circuit. In FIG. 17, the conventional distortion-compensated amplifying circuit includes an input terminal 601, an output terminal 602, a power distributor 603, a delay circuit 604, a distortion generating circuit 605, a variable attenuator 606, a phase changer 607, a power combiner 608, a power amplifier 609, a directional coupler 610, and a controller 611.
In the above-structured distortion-compensated amplifying circuit, a carrier signal supplied from the input terminal 601 is distributed into two by the power distributor 603. Based on one of these two carrier signals obtained by distribution, the distortion generating circuit 605 generates a distortion signal. This distortion signal is adjusted in amplitude and phase by the variable attenuator 606 and the phase changer 607, respectively, and is then given to the power combiner 608. The other one of the two carrier signals obtained by distribution is delayed by the delay circuit 604, and is then forwarded to the power combiner 608. The power combiner 608 combines the distortion signal and the carrier signal with each other for input to the power amplifier 609. The power amplifier 609 amplifies the received signal for output to the output terminal 602.
Provided between the power amplifier 609 and the output terminal 602 is the directional coupler 610, where part of the signal supplied by the power amplifier 609 is branched to the controller 611. The controller 611 controls the variable attenuator 606 and the phase changer 607 so that the distortion signal supplied to the power combiner 608 becomes equal in amplitude and opposite in phase to intermodulation distortion (hereinafter simply referred to as xe2x80x9cdistortionxe2x80x9d) that occurs when the power amplifier 609 amplifies the carrier signal.
As described above, in the distortion-compensated amplifying circuit of FIG. 17, a distortion signal is generated by the power amplifier 609 so as to be equal in amplitude and opposite in phase to distortion that may occur when the power amplifier 609 amplifies the carrier signal. The distortion signal is then added in advance to the carrier signal to be supplied to the power amplifier 609. This means that a distortion component equal in amplitude and opposite in phase to possible distortion is supplied to an input side of the amplifier. With this, distortion that occurs in the power amplifier 609 is reduced. Such a distortion compensation scheme is called a pre-distortion technique, which is disclosed in Japanese Patent Laid-Open Publication No. 2000-261252, for example.
However, the conventional distortion-compensated amplifying circuit adopting the pre-distortion technique as disclosed in FIG. 17 has the following problems. The distortion signal to be supplied from the distortion generating circuit 605 via the variable attenuator 606 and the phase changer 607 to the power amplifier 609 includes a carrier component as well as a distortion component. This carrier component is also adjusted in amplitude and phase in the variable attenuator 606 and the phase changer 607. Therefore, the power combiner 608 will receive a carrier component opposite in phase to the carrier signal received via the delay circuit 604. Therefore, part of the carrier signal is cancelled by the carrier component opposite in phase thereto, thereby causing attenuation in carrier level. Such attenuation in carrier level requires an additional amplifier in order to compensate for lost power to satisfy a desired carrier level.
Moreover, in the circuit as illustrated in FIG. 17, amplification of the received distortion component and suppression of the distortion are simultaneously carried out at the power amplifier 609. Therefore, in practice, it is very difficult to obtain a sufficiently large amount of distortion.
The present invention is made in order to solve the above problems. An object of the present invention is to provide a distortion-compensated amplifying circuit capable of suppressing a larger amount of distortion, compared with conventional distortion-compensated amplifying circuits, without attenuation in level of a carrier component.
The present invention has the following features to attain the object mentioned above.
A first aspect of the present invention is directed to a distortion-compensated amplifying circuit for amplifying a signal and compensating for distortion that occurs at a time of amplifying the signal, including:
two amplifying sections placed in parallel each for performing a signal amplifying process;
a first combining and distributing section supplied with an original signal including a carrier component and a first distortion signal having a frequency equal to a frequency of distortion that occurs when the original signal is amplified by each of the two amplifying sections, the first combining and distribution section for combining the original signal and the first distortion signal together and then distributing the combined signal into two signals for output to the two amplifying sections;
a second combining and distributing section for combining the two signals supplied from the two amplifying sections and then distributing the combined signal into two signals; and
a combining section for combining the two signals supplied from the second combining and distributing section for output, wherein
each of the first and second combining and distributing sections is a hybrid circuit that outputs two signals with a predetermined phase difference.
In the above first aspect, two amplifying sections are placed between first and second hybrid circuits to form balanced circuitry. When the first hybrid circuit is supplied with the original signal and the distortion signal, the second hybrid circuit outputs two signals: a signal including only a distortion component delayed in phase with respect to the received distortion signal, and a signal including a carrier component delayed in phase with respect to the received original signal and a distortion component advanced in phase with respect to the received distortion signal. When these output signals are combined, at least part of the distortion components included therein are canceled with each other because these components are out of phase. Consequently, distortion included in the combined signal is suppressed (this suppression is an effect of the post-distortion technique). In this case, the carrier component is not cancelled because it is included in only one of the two output signals. Therefore, attenuation in carrier level can be prevented.
This distortion suppression effect achieved by the post-distortion technique becomes larger, as the distortion components included in the two signals produced from the second hybrid circuit are closer to being opposite in phase (having a phase difference of 180 degrees) and to being equal in amplitude to each other. When these distortion components become opposite in phase and equal in amplitude to each other, a maximum suppression effect can be obtained. Therefore, as described below in a fourth aspect, when 90-degree hybrid circuits are used, the distortion signal supplied to the first hybrid circuit is preferably shifted in phase by 180 degrees from distortion that occurs in the amplifying sections. Moreover, as described below in a sixth aspect, it is most preferable that the distortion signal be equal in amplitude to the distortion that occurs in the amplifying sections.
That is, as mentioned above, when the distortion signal supplied to the first hybrid circuit is shifted in phase by 180 degrees from the distortion that occurs in the amplifying sections, the received distortion signal and the distortion have a phase difference of 90 degrees, and therefore these signals do not interfere with each other. In view of this, the second hybrid circuit outputs two signals: a signal including only a distortion component delayed in phase by 90 degrees with respect to a first distortion signal supplied to the first hybrid circuit, and a signal including a carrier component delayed in phase by 90 degrees with respect to the original signal supplied with the first hybrid circuit and a distortion component advanced in phase by 90 degrees with respect to the first distortion signal supplied with the first hybrid circuit. Then, when these two signals are combined, the distortion components opposite in phase to each other are completely canceled if they are equal in amplitude to each other.
In the first aspect, the post-distortion technique carried out for suppressing distortion is such that the original signal and the distortion signal are amplified by the amplifier including two balanced hybrid amplifying sections (that is, differential amplification is carried out) so as to have a phase difference. Then, the amplified original signal and distortion signal are combined. In this case, a process of amplifying the distortion signal and a process of suppressing distortion that occurs when the original signal is amplified are performed separately. Therefore, it is possible to obtain a larger amount of suppression of distortion, compared with a conventional distortion-compensated amplifying circuit using the pre-distortion technique.
Still further, the second hybrid circuit outputs a signal including only the distortion component. Therefore, based on the power of this signal, the amplitude and phase of the distortion signal supplied to the first hybrid circuit can be easily performed as described below in a seventh or twelfth aspect.
According to a second aspect based on the first aspect, the distortion-compensated amplifying circuit further includes a signal input section for inputting the original signal and the first distortion signal to the first combining and distributing section.
In the above second aspect, the signal input section supplies the above-mentioned original signal and first distortion signal to the first combining and distributing section.
According to a third aspect based on the second aspect, the signal input section includes a phase adjusting section for adjusting a phase of the original signal and/or a phase of the first distortion signal to be supplied to the first combining and distributing section.
In the above third aspect, the phase adjusting section adjusts the phase of the original signal and/or the phase of the first distortion signal.
According to the fourth aspect based on the third aspect, each of the first and second combining and distributing sections is a 90-degree hybrid circuit that outputs the two signals with a phase difference of 90 degrees, and
the phase adjusting section adjusts the phase of the original signal and the phase of the first distortion signal so that the first distortion signal to be supplied to the first combining and distributing section has a phase difference of 180 degrees with respect to the distortion that occurs when the original signal is amplified by each of the amplifying sections.
In the above fourth aspect, the distortion components included in the two signals supplied by the second hybrid circuit are opposite in phase to each other. Therefore, a high distortion suppression effect can be obtained.
According to a fifth aspect based on the fourth aspect, the signal input section further includes an amplitude adjusting section for adjusting an amplitude of the first distortion signal to be supplied to the first combining and distributing section.
In the above fifth aspect, the amplitude adjusting section adjusts the amplitude of the first distortion signal.
According to the sixth aspect according to the fifth aspect, the amplitude adjusting section adjusts the amplitude of the first distortion signal to become equal to an amplitude of the distortion that occurs when the original signal is amplified by each of the amplifying sections.
In the above sixth aspect, the distortion components included in the two signals supplied by the second hybrid circuit are opposite in phase and equal in amplitude to each other. Therefore, the highest distortion suppression effect can be obtained.
According to the seventh aspect based on the sixth aspect, the second combining and distributing section outputs
a signal only including a distortion component delayed in phase by 90 degrees with respect to the first distortion signal supplied to the first combining and distributing section; and
a signal including a carrier component delayed in phase by 90 degrees with respect to the original signal supplied to the first combining and distributing section, and a distortion component advanced in phase by 90 degrees with respect to the first distribution signal supplied to the first combining and distributing section, and
the signal input section further includes a control section for controlling the phase adjusting section and the amplitude adjusting section based on a power of the signal including only the distortion component.
In the above seventh aspect, the control section detects the power of one of the signals (that includes only the distortion component) supplied by the second hybrid circuit. Based on the detection results, the control section controls the phase adjusting section and the amplitude adjusting section. With this, even if the amplitude and phase of the distortion that occurs in the amplifying sections are varied due to changes in environmental temperature, for example, it is possible to follow the changes, thereby keeping the high distortion suppression effect.
According to an eighth aspect based on the second aspect, the signal input section includes
a distributing section for distributing the original signal into two signals; and
a first distortion generating section for generating the first distortion signal based on one of the two signals distributed by the distributing section.
In the above eighth aspect, the original signal is distributed into two signals and, based on one of the two signals, a first distortion signal is generated. To the first combining and distributing section, the other of the two signals and the first distortion signal are supplied.
According to a ninth aspect based on the second aspect, the signal input section includes a distortion adding section for adding, to the original signal, a second distortion component having a frequency equal to a frequency of the distortion that occurs when the original signal is amplified by each of the amplifying sections.
In the above ninth aspect, the distortion adding section adds a second distortion component to the original signal. The first hybrid circuit is supplied with this original signal added with the second distortion component and a distortion signal including the first distortion component. The first hybrid circuit distributes each of the received signals into two signals, and outputs these signals with a phase difference of 90 degrees to each amplifying section. When amplifying the original signal added with the second distortion component, each amplifying section performs a process of suppressing distortion with the pre-distortion technique. As a result, the amount of distortion is reduced, compared with a case where the second distortion component is not added. With this, the process of suppressing distortion is performed in the combining section with the post-distortion technique and also in each amplifying section with the pre-distortion technique. Thus, a higher distortion suppression effect can be obtained.
Furthermore, with the combination of the pre-distortion and post-distortion techniques for suppressing distortion, the level of the first distortion signal subjected to post-distortion can be reduced, compared with a case where only the post-distortion technique is performed for suppressing distortion. As a result, it is possible to obtain effects similar to those obtained when the amount of attenuation of the carrier components are reduced.
According to a tenth aspect based on the ninth aspect, the signal input section further includes a phase adjusting section for adjusting a phase of the original signal added with the second distortion component and/or a phase of the first distortion signal to be supplied to the first combining and distributing section.
In the above tenth aspect, the phase adjusting section adjusts the phase of the original signal added with the second distortion and/or the phase of the first distortion signal.
According to an eleventh aspect based on the tenth aspect, each of the first and second combining and distributing sections is a 90-degree hybrid circuit that outputs the two signals with a phase difference of 90 degrees, and
the phase adjusting section adjusts the phase of the first distortion signal and the phase of the original signal so that the first distortion signal to be supplied to the first combining and distributing section has a phase difference of 180 degrees with respect to the distortion that occurs when the original signal added with the second distortion component is amplified by each of the amplifying sections.
In the above eleventh aspect, the distortion components included in the two signals supplied by the second hybrid circuit are opposite in phase to each other. Therefore, a high distortion suppression effect can be obtained.
According to the twelfth aspect based on the tenth aspect, the signal input section further includes an amplitude adjusting section for adjusting an amplitude of the first distortion signal to be supplied to the first combining and distributing section.
In the above twelfth aspect, the amplifying adjusting section adjusts the amplitude of the first distortion signal.
According to a thirteenth aspect based on the twelfth aspect, the amplitude adjusting section adjusts the amplitude of the first distortion signal to become equal to an amplitude of the distortion that occurs when the original signal added with the second distortion component is amplified by each of the amplifying sections.
In the above thirteenth aspect, the distortion components included in the two signals supplied by the second hybrid circuit are opposite in phase and equal in amplitude to each other. Therefore, the maximum distortion suppression effect can be obtained.
According to a fourteenth aspect based on the thirteenth aspect, the second combining and distributing section outputs
a signal only including a distortion component delayed in phase by 90 degrees with respect to the first distortion signal supplied to the first combining and distributing section; and
a signal including a carrier component delayed in phase by 90 degrees with respect to the original signal supplied to the first combining and distributing section, and a distortion component advanced in phase by 90 degrees with respect to the first distribution signal supplied to the first combining and distributing section, and
the signal input section further includes a control section for controlling the phase adjusting section and the amplitude adjusting section based on a power of the signal including only the distortion component.
In the above fourteenth aspect, the control section detects the power of one of the signals (that includes only the distortion component) supplied by the second hybrid circuit. Based on the detection results, the control section controls the phase adjusting section and the amplitude adjusting section. With this, even if the amplitude and phase of the distortion that occurs in the amplifying sections are varied due to changes in environmental temperature, for example, it is possible to follow the changes, thereby keeping the high distortion suppression effect.
According to a fifteenth aspect based on the ninth aspect, the signal input section further includes an amplitude adjusting section for adjusting an amplitude of the first distortion signal to be supplied to the first combining and distributing section.
In the above fifteenth aspect, the amplifying adjusting section adjusts the amplitude of the first distortion signal.
According to a sixteenth aspect based on the fifteenth aspect, the amplitude adjusting section adjusts the amplitude of the first distortion signal to become equal to an amplitude of the distortion that occurs when the original signal is amplified by each of the amplifying sections.
In the above sixteenth aspect, the distortion components included in the two signals supplied by the second hybrid circuit are equal in amplitude to each other. Therefore, a high distortion suppression effect can be obtained.
According to a seventeenth aspect based on the sixteenth aspect, the second combining and distributing section outputs
a signal only including a distortion component delayed in phase by 90 degrees with respect to the first distortion signal supplied to the first combining and distributing section; and
a signal including a carrier component delayed in phase by 90 degrees with respect to the original signal supplied to the first combining and distributing section, and a distortion component advanced in phase by 90 degrees with respect to the first distribution signal supplied to the first combining and distributing section, and
the signal input section further includes a control section for controlling the phase adjusting section and the amplitude adjusting section based on a power of the signal including only the distortion component.
In the above seventeenth aspect, the control section detects the power of one of the signals (that includes only the distortion component) supplied by the second hybrid circuit. Based on the detection results, the control section controls the phase adjusting section and the amplitude adjusting section. With this, even if the amplitude and phase of the distortion that occurs in the amplifying sections are varied due to changes in environmental temperature, for example, it is possible to follow the changes, thereby keeping the high distortion suppression effect.
According to an eighteenth aspect based on the ninth aspect, the signal input section further includes
a distributing section for distributing the original signal into two signals; and
a first distortion generating section for generating the first distortion signal based on one of the two signals distributed by the distributing section, and
the distortion adding section generates the second distortion component based on another of the two signals distributed by the distributing section, and adds the generated second distortion component to the other of the two signals.
In the above eighteenth aspect, the original signal is distributed into two signals and, based on one of the two signals, a first distortion signal is generated. Also, a second distortion component is generated based on the other of the two signals, and is then added to the other signal. The first combining and distributing section is supplied with the first distortion signal and the other signal added with the second distortion component.
According to a nineteenth aspect based on the ninth aspect, the signal input section further includes:
a first distributing section for distributing the original signal into two signals;
a first distortion generating section for generating the first distortion signal based on one of the two signals distributed by the first distributing section from the original signal; and
a second distributing section for distributing the first distortion signal generated by the first distortion generating section into two signals, and
the distortion adding section adds, as the second distribution component, one of the two signals distributed by the second distributing section from the first distortion signal to another of the two signals distributed by the first distributing section from the original signal.
In the above nineteenth aspect, the original signal is distributed into two signals and, based on one of the two signals, generates a first distortion signal. The first distortion signal is further distributed in two signals, and one of these two signals is added as a second distortion to the other original signal. The first combining and distributing section is supplied with the first distortion signal and the other original signal added with the second distortion component.
Twentieth, twenty-second, twenty-fourth, and twenty-sixth aspects correspond to distortion-compensated amplifying circuits according to first to fourth embodiments, respectively.
According to twenty-first, twenty-third, twenty-fifth, and twenty-seventh aspects based on the twentieth, twenty-second, twenty-fourth, and twenty-sixth aspects, respectively, a control section is provided to control the vector adjusting section based on one of the signals supplied by the second power combining and distributing section.
Twenty-eighth through thirty-first aspects of the present invention are directed to feed-forward type amplifiers using any of the distortion-compensated amplifying circuits according to the twentieth, twenty-second, twenty-fourth, and twenty-sixth aspects.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.